The closest prior art known to the inventors is illustrated in FIGS. 1 and 2. The cargo shuttle or yard trailer illustrated therein, like the present invention, was designed to transport prefabricated building modules from the end of an assembly line to a highway semitrailer or temporary storage cradle located in a storage or shipping area some distance from the end of the assembly line. Each module is roughly twenty-four feet long, twelve feet wide and twelve feet high at its taller end and weighs approximately five tons. The old yard trailer comprised a generally U-shaped, wheeled frame A that could be pivotally attached to a fork lift at the closed end thereof. Two relatively spaced apart vertical columns B were provided on each of side of the frame. As indicated in FIG. 2, each of the vertical columns was formed with a longitudinally coextensive channel C that opened toward an aligned column on the opposite side of the trailer. A block D was slidably mounted in each of the channels and a load-bearing foot member E was pivotally attached to each of the blocks. The sliding channel blocks and attached feet could be raised and lowered by means of hydraulically-actuated chain and pulley assemblies F mounted on each side of the frame. The operator could position the trailer, via the forklift, so that the sides of the frame were disposed along opposite sides of a module at the end of the assembly line and the feet were in their lowest possible positions in the channels. Upon activating the hydraulic units that controlled the chains, channel blocks and feet, the operator could lift the module off of the assembly line and carry it to a shipping or storage area located elsewhere on the plant grounds, whereupon it would be lowered onto a highway semitrailer or a temporary cradle.
There were a number of problems with the old yard trailer. First, the channel block in each of the columns was subject to a great deal of wear. Secondly, the old equipment could not raise the modules high enough to clear the ends of a newly designed semitrailer. In addition, it became difficult to position the feet close enough to the ground to fit underneath the base of the module after a new, lower profile roller or trolley was provided to carry the modules along the assembly line. Finally, and perhaps most importantly, the modules were being damaged by the old loader. Little space was provided between the vertical columns of the loader and the sides of the module so that the load-bearing feet could be as short as possible. After a period of use, the columns tended to become slightly inwardly angled under the force of the load, thereby eliminating what little space was provided originally for the modules. Consequently, the sides of the module would scrape against the stationary vertical columns as the module was raised and lowered.
While the present loader retained the generally U-shaped design of the old loader's frame, as well as the ability to be powered, directed and controlled, via mechanical, electrical and hydraulic connections, with a forklift or other auxiliary vehicle, the means by which the modules are raised and lowered is substantially different, as indicated below. As a result, the aforementioned problems of the prior art have been eliminated or reduced substantially.